Question

Write the electronic configuration of chlorine (atomic number 17). Explain its position in the periodic table and write its valency.

Hint:

Halogens like chlorine have 7 valence electrons and are highly reactive because they need one more electron to achieve a stable octet. This makes them strong oxidizing agents and reactive in forming ionic or covalent compounds.

Answer 1

Step 1: Electronic configuration of chlorine. The atomic number of chlorine is 17, which means it has 17 electrons. The electronic configuration is written by filling the orbitals in the order of increasing energy: \[ \text{Chlorine (Cl)}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^5 \] This configuration indicates: - 2 electrons in the first shell (1s), - 8 electrons in the second shell (2s and 2p), - 7 electrons in the third shell (3s and 3p).
Step 2: Position of chlorine in the periodic table. - Chlorine is a member of Group 17 (also known as Group VIIA), which is the halogen group. - It is in the third period of the periodic table. - Chlorine has a total of 7 valence electrons in its outermost shell (3p^5), which makes it highly reactive, especially in forming salts with metals.
Step 3: Valency of chlorine. - The valency of chlorine is 1. This is because chlorine needs one more electron to complete its octet and achieve the stable electronic configuration of argon (a noble gas). - Therefore, chlorine can gain one electron to form a negatively charged ion (Cl⁻), or it can form a covalent bond by sharing one electron with another atom (such as hydrogen in HCl).
Conclusion: The electronic configuration of chlorine is \( 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^5 \), it belongs to Group 17 (halogens) and the third period, and its valency is 1.